The long term goal of this research is to establish an experimental system for predicting physicochemical stress-modulation of choline transport across the cerebrospinal fluid (CSF)-blood barrier, i.e., the choroid plexus epithelium. The objective of this proposal is to characterize modulation of choroid plexus choline transport by zinc and cadmium as a means to predict the potential for heavy metals to alter choline availability in the brain. Choline is a polar constituent of membrane phospholipids and an immediate precursor to acetylcholine, the neurotransmitter for central cholinergic pathways crucial in neural control of behaviors such as sleep-wake cycling and learning/memorization. Choline availability is also critical for normal brain development; deficiency in fetal or neonate rats results in developmental and behavioral abnormalities and learning/memory deficits that may persist in the adult. Symptoms of heavy metal toxicity in neonate animals and children include significant reduction in learning/memory skills and behavioral disorders. Cadmium and other metals may directly inhibit central cholinergic neuron activity. However, these metals may also compromise cholinergic activity by reducing choline availability. Heavy metal exposure has been shown to reduce choline levels in the midbrain. Metals such as cadmium and zinc accumulate within the choroid plexus, which actively transports choline out of the brain. These heavy metals may stimulate choroidal choline transport, enhancing choline removal and decreasing its availability in the brain. The proposed studies will test the hypothesis: Choline is actively transported across the CSF-blood barrier and, therefore, modulation of this active transport process by a chemical stress, i.e., exposure to heavy metals, may alter choline availability in the brain. This hypothesis will be directly tested using a primary culture system of choroidal plexus epithelial cells from neonate rats. Radiotracer, molecular biology, immunochemistry and fluorescence microscopy techniques will be used to meet the following specific aims: i.) characterize cellular mechanisms that mediate choline transport across the CSF-blood barrier; ii.) examine zinc-induced modulation and thermotolerance of choroidal choline transport; iii.) characterize heat-shock protein- dependent modulation of choline transport by cadmium. A greater understanding of the energetics and modulation of choline transport across the CSF-blood barrier may permit more effective management and treatment of metal neurotoxicity and other central nervous disorders that involve changes in free choline levels, such as organophosphate poisoning.